Process for manufacture of enameled leathers.



R. M. HUNTER.

PRocEss Fon MANuFAcTuRE or ENAMELED LEATHERS.

APPLICATION FILED FEB. 9. |910.v 1, 182,01 3. Patented May 9,1916.

2 SHEVETSHE I IIIVEIITUR WITIIESSES R. M. HUNTER.

PROCESS FOR MANUFACTURE 0F ENAMELED LEATHERS.

1 APPLICATION FILED fsa. 9. |910.

Patented May 9, 1916.

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VIITIESSES INVEIITDR j )XMK ,:0/ 0/2/ my UNITED STATES PATENT OFFICE.

RUDOLPH M. HUNTER, OF PHILADELPHIA, PENNSYLVANIA.

PROCESS FOR MANUFACTURE OF ENAMELED LEATHERS.

Specification of Letters Patent.

Application filed February 9, 1910. Serial No. 542,880.

fully set out in the following specification.

and shown in the accompanying drawings which form a part thereof A My invention has reference broadly to the preparation of leathers with a polished or enameled coating such as.y provided on patent-leather, enamel-kid, etc., in which the surface, of the leather is first dyed or colored and subsequently enameled y a coating of varnish having proper qualities.

I will describe my invention more particularly with respect to the manufacture of enameledkid, and from which description, the general characteristics of my improved methods for leathers, as well as the apparatus for the purpose of carrying it commercially into effect, will be fully understood. Any form of leather with an enameled surface may be produced bv my improved process and apparatus and any modification in appearance will be due to variations in the character of the leather, coloring and varnishing thereof, rather than to the difference of the method or means employed in its produc-A In the production of enameled-leather, it has heretofore been the practice to first stretch the skin on'a frame and then coat the skin with a daub, which may consist of a collodion compound made of gun-cotton and amyl acetate, which acts as a filler and water-proof coating, the said daub being colored by nigrosin or otherwise to give the black or colored ground for. the enamel. The leather, so'treated, is allowed to dry, preferably in the sun for sixhours, or lacking sunshine. in a closed oven heated to about 120 degrees Fahr. for a like period, and is then rubbed down with pumice stone to make its coated 'surface smooth. The leather is then varnished with a solution of boiled linseed oil thinned down with turpentine and colored with YPrussian blue ground in oil, or other coloring ingredients where making enameled' the patent-leather is to be colored. The leather, in its varnished condition, is then put lnto an oven and baked at a temperature of about 140O or upward Fahr. for thirty to forty-eight hours, the oven being a closed affair having no outlets or inlets and heated by steam pipes. The baking being completed, the leather is then removed from the oven, and is next exposed to the sun in the open air until all tackiness is removed. vThis latter operation usually requires from thirtysix to seventy-two hours additional. The operation of pumice-stoning, varnishing, baking and sunning may be repeated if so desired as often as required to secure the degrees of finish to the patent-leather which may be demanded. Experience has shown that serious objections are found in this process, which may be briefly referred to as follows The time required for the drying of the daub coating is undesirably long, being not less than six and frequently approximating ten hours, and is objectionable in that it depends upon atmospheric conditions, or those involving a high temperature in a closed draftless oven with the result that the leather is materially injuredv in texture and frequently burned. The time required to bake the varnished leather is excessively. long, and yet from the nature of the process, it has not heretofore been possible to shorten it. The baking of the leather in the closed oven maintains the turpentine or other solvent in. contact with the leather for an objectionably long period, and moreover, because of the volatile nature of the turpentine, it rises to the higher part of the furnace, with the result that the skins which are near the bottom or next the heating coils are baked to a greater and more dry condition than the skins adjacent to the Patented May 9, 1916. i

upper part of the drierchamber, thereby the oven derives its heat. These skins are l either rendered useless or must be sold in the does not occur for considerable periods at.

certain times of'theyear. So V troublesome has this been during some years that it has been impossible' for manufacturers- -to fill their orders, and not infrequently this trouble has caused ruination of the manufacturer. The second objection to the sunning process lies in the fact thattheframes containing the stretched and vbakedv skins are required to be taken from theovens Vand placed in the open air sov as' to be `acted upon by the sun, necessitating great labor, loss of time, and causing much loss by in- `jury to the skins and frames by careless handling; and where the varnishing is per.- forrned a number of times on the same skins, the loss of time from this cause is very im'- portant, because the transferring of the l frames is largely done skilled workmen who, at other times, are preparing the skins.

.And further, objection lies in the fact that at certaintimes' of the year storms are liable to occur unexpectedly, and if,l atl such ,t1mes, the skins. are. not quickly removed Istant worryl and anxiety'to the .manufac- I turer and frequently of very great loss.` A

into shelter, they willbe injured by the rain; v

such state of affairs being a; source-of con- 'v still furtherllrobjection to this 'part ofthe process liesinzt'he fact that the skins, being tacky, very frequently become 'injured owing to the blowing of dust on windyv days, which -dust adheres to the surface and dull's the leather. Furthermore, on Vvery hot dry days thevarnished surface of the leather is liable to become discolored by `what are v known as sunspots, a' condition which destroys .its salability.

z The foregoing are the 'objectionable' features incident to the present methg" d "of manufacturing enameled leathenandwhich @proximately. twenty-five'- fhours,v tl'le lvarit is the object of my invention .to overcome. The 'objectscof my i nvention,'not"only are to overcome each and all of the above existing objections, but .also to greatly increase the output'of a given number of ovens, jto

reduce-the number ofskilled workmen necessary 'for}.a y'givengutputfin skins,'to-produce absolute uniformity inthe character .of all the skins treated, to greatly reduce the time required to complete the ena-melin'g of the skins,`toeliminate' all handling of the skins after beingvarnished andup to the com-V pletion of the-process, to prevent any burn; ing or over-baking, to provide capacity. for producing the enameled leather-irrespective -of the -condition of the atmosphere and to insure the manufacturer being able to regularly lproduce a given number of Aenameled skins within any given period whereby vhe perature of120" .'Fahr. exposed in theopen air while theyfare still 'f being pu'xriieLstoned, is- .varnished and' remay carryon his business with every degree of confidence. Y

' The object 'of my invention is further, to greatly --cheapen the cost of' enameling the skins, and. as the result of the advantages above' enumeratedand byfreason of the facts hereinafter set out, I have found, by actual experience, that the cost heretofore required to enamel the skins, (exclusive of the cost of the skins) may be reduced fifty per cent'. by use of my improved process and apparatus, said savingA equaling 'upward of $55,Q00,000 upon the present enameled leather output inthe United States alone; and moreover, the said saving may be had while producing a better finished and more marketable product.

My invention consists in 'a method of treating the leather and in the means em' ployed therefor, whereby said method may be carried into commercial effect, which method and means are more fully described hereinafterand defined in the claims.

In general, my improved method may be stated `to consist .in first drying the stretched leather, after it has been coated with the filling and coloring 'matter or daub, within an oven or closed chamber through which acu-rrent of heated air `is caused to Slowly pass",*thesame being preferably allowed togo to waste after acting upon the leathenff This operation requires approximately three hours and under a tem- Thedried daub c oatedjleathe'ris then-removed, and after Vinserted ntotheao'ven, and'subieoted to a forced continuous 'circulation of preferably the same heated'airfat temperatures prefervnished leather'iisbroughttoa baked con-A dition and comparatively free from the vlatile,l turpentine', and it. is then treated to lcirculating air-fata `temperature of approximately145 degreesrFahnor higher Vfor nine hours` more, result-ing iii=acondition of dry-A ness in which there willfbe'. some tackiness, which is removedfby then reducing the temperaturecf the oventofatmospheric temperatureand preferably not over 95` degrecs-Fahr., `sind performing this drying by air takenffrom outside of .the building and, 'after actingupon the'fsskinsyallowing it to escape, soiasrto'causelarge quantities of dry cool air'to pass over the-surface of the varlthe turpentineand-chill the' surface of the enamel. This lattertreatinent would ordi-- -nishedleatherto remove the last trace of narily be carried on for three hours, after which time the frames may be withdrawn from the oven and the skins will be found to be free from all tackiness and with a most perfect luster and uniform in character. The circulation of the air insures all the skins being treated alike, and prevents excessive heating and burning of the skins next to the heating coils. No handling of l0 the skins through the entire baking and drying processes is required, as all actual manipulations are carried on with respect to the circulation of the air and the temperatures under which it is maintained.

The preliminary drying process for the drying of the daub coating may be omitted if desired, and the said drying be `carried on in warm rooms or in the open atmosphere, if so preferred; though it is far more desirable to dry the same in the ovens under the conditions above specified, namely the circulation of heated air over the coated leather without re-circulating the same air.

It will be understood that in giving tem' peratures and'time of treatments, I have given those which I have found most advantageous, and said data are given by way of illustration and not as a limitation upon my invention.

My invention will be better understood by reference to the drawings, in which Figure 1 is a transverse sectional elevation of an oven embodying my invention and in which to carry my improved method into practice, the same being taken on line wof Fig. 2; Fig. 2 is a longitudinal sectional elevation of the same taken. on line jl/-y of Fig. 1; Fig. y3 is a plan view of a plurality of my improved ovens with associated apparatus for commercially carrying my process into practice upon a large scale; Fig. 4 is an elevation of the same; Fig. 5 is a cross section on line s-s of Fig. 4 showing the inlet valves for the ovens; and Fig. 6 is a similar cross section on line t-t showing the outlet valves for the ovens.

I will lirst describe the construction and operation ofthe single oven shown in Figs. 1 and 2 and then consider the use of the apparatus and method when employing the plurality of ovens as shown in Figs. 3 to 6 inclusive. Y

The oven consists essentially of a chamber 4 2 having heat insulating walls 3 about it of o with removable hinged doors 19, each of small vertical height, arranged one above the other, so that the front may be gradually closed up and made comparatively tight as the oven receives the frames with the skins stretched upon them. These doors may be made in any suitable manner, and I do not as to their construction. vThe lower part of the chamber 2 may be provided with heating coils 12 through which steam may be passed and controlled by means of a hand valve 20 arranged immediately outside of the oven. The steam coils 12 are arranged within the compartment 8 at the bottom of the oven and into Which air is supplied at one side by a conduit 10, which may be provided with a suitable valve 11 to control or shut olf the supply of air. The other side of the compartment 8 is open, as at 9, said opening extending along one side of the oven. Each of the interior side walls of the oven are provided with upright studs 4, and upon these are secured horizontal angle irons 6, arranged parallel and at a distance above each other to form guides upon which the leather supporting frames 7 rest. means of these guides, the frames 7 are enabled to be shoved into position and be supported at a short distance above each other. The skins to be treated are stretched upon or secured to the open frames 7 in any of the well known manners employed in the manufacture of enameled or patent-leather.

, The studs 4 provide, as it were, a series of across between the various frames 7 and into the vertical passages 5 at the other side of the oven and thence upward, escaping at the top into a header 13, from which flues 14 and 15 open, the former leading to the' atmosphere, or to a chimney or other draft producing device, such as a fan, and the latter leading to means for circulating the air over again through the oven as described hereinafter. A valve 16 is so pivoted as to control the entrance of air to either of the lues or conduits 14 and 15. The valve shown is pivoted and adapted to be oscillated by a hand rod 18 and is counter-weighted at 17, so that when it is thrown into the position indicated in full lines, or into the position indicated in dotted lines, the said counter- Weight 17 will hold the valve in such assumed position. While the upper end of the passage or lues 5 at one side of the oven discharges the heated air into the header 13 at the top of the oven, the corresponding iues or passages 5 at the other side of the oven Ireceives the hot air from the open end ByY 9 of the steam heated compartment d8 at the 7 and their skins, so that the'said skins are treated both above and below to currents` of air, it being understood that the frames are of the usual open construction which expose both sides of the stretched skins. It will, further, be observed that all of the skins are subjected to air currents to substantially the same extent, because they resistance to the flow of the air through the oven is substantially the same with respect to every frame within it. In an oven of this character the skins may be stretched completely over the entire openings in the frames 7, such as would sometimes occur where side leather was employed, as distinguished from kid, and yet both sides of the skin would be equally heated and dried. Furthermore, the air is carried away from the oven immediately after it has become impregnated with the turpentine or other volatile gases expelled by the heat, so that drying is performed in a speedy manner and with great uniformity in respect to each and ever skin in the entire oven. From this it ig evident that, unlike the ovens formerly employed in the manufacture of patent-leather, thereis no possibility of the lower treated skins .becoming the heating coils, or of the upper skins becoming over-saturated or half dried because of the accufnulation of turpentine from the varnish or volatile gases from the daub in the upper part of the oven. Furthermore, the action is such, that there is no tendency of dripping of the tur entine and varnish from one s in to the ot er, because the volatile substances which may tend to 'form drippings are rapidly conveyed away as quickly as formed, and the result, in practice is, that all of the skins are uniformly dried and said drying is accomplished'in a speedy and efficient manner. In view of the special manner of circulating the air, andV broadly, because of the fact that the air is circulated and not allowed to remain in a ystagnant form in the oven, as heretofore,

the drying operation of patent-leather is accomplished in a fraction of the time which has heretofore been required; and moreover, the leather when taken from the oven, is devoid of any tackinessf a condition which has never before been possible Iunder the methods formerly employed wherein the treatment in the oven is carried on without the elimination of the volatile turpentine and other gases produced by action of the oven upon the prepared leathers While I prefer to provide the compartment 8 at the bottom of the oven, to insure the heated air passing over the'coils'12 and into the vertical passa s 5 before being a1- lowed to flow upwar', it is evident that, broadly considered, this compartment might dried up or burned by being too neartreated to the daub perature,

tile vapors or gases 'through it, the daub be dispensedy -with where the frames 7 have their lopenings only partly covered with leather, such as when kid-skins arebeing enameled, because in that case,l there are considerable openings through which the heated air may pass upward through the ovenchamber and escape by the lues 14and 15, asvrequired. I have found that the vertical passages 5 and the lateral openings between the guides 6 may be dispensed with and reasonably fair results secured whenever the skins to be enameled cover'only -a portion of the openings in theframe 7 as r oven is considered far superior to the cony,

struction in which the oven is simplylsupplied with the inlet and outlets, respectlvel'y,

at the bottom and top andv relying on the j passage of the air through the frames, and I prefer'in all cases to employ thelty'pe of oven In drying out the here shown and fully described.

skins `which have been coating after they arestretched upon the frames 7, the said frames are placed in adjusted to the position shown 1n Fig. 1. Air is then supplied by the duct 10 through the oven andthe valve 16 is the va1vel1 andl caused to pass'over the heatingcoils' 12 to attain the desired temthence through the oven, as 1nd1- cated by the arrows,

from the daub coating on the various'skins, livering the* said vapors or. gases 1nto the flue 14, which may lead dlrectly into .the chimney of the factory, or may dehyer `into any suitable apparatus for condensing and collecting the vapors. In th1s part of .the process, the current of air and the extent of its heating is controlled with a View orf` speedy drying. consistent i.

insuring the most with proper maintenance of the. conditions of the skins and the daub, and th1s`regu lation may be performed by natural draft or carrying off the vola- K los said air current dethe control o f the valve 11 and the steam valve 20. The f 12u i by means of a blower and l may be heated or not as desired, before being delivered to compartment 8. In practice, I have foundy that, by the employment of my improved oven maintained at a working temperature of about degrees Fahr. and a slowly circulating current of air coating maybe dried in a moi perfect manner within three hours,

instead f requiring the six hours or more Crt heretofore necessary in sun drying under the old method. After the daub coating has been thoroughly dried it is pumice-stoned to impart to it the desired smoothness, and the stretched leather is then varnished and reinserted into the oven. When the oven has been filled with frames 7 containing varnished skins, the valve 16 is adjusted t0 the dotted position, and the air, which enters by the duct 10, is heated to the desired temperature in passing over the coils 12 and then circulated through the oven, as indicated by the arrows in F ig. 1, so that all of the skins are equally treated. The volatile vapors of turpentine which are given off from the varnish on the skins are conveyed by the air into the header 13, and thence by the duct 15 to a suitable condenser, and

vthence to a heater, and back to the duct 10,

as will be later' more fully described. The volatile turpentine vapors are thus removed from the oven chamber 2 and away from the skins as soon as formed, and by means of the condenser are taken out of the circulation. The air may thus be circulated over and over again through the oven chamber until the proper degree of drying of the varnish has been secured. The temperature of the air must not be raised too high at the preliminary operation of drying for the reason that there will be a tendency to form bubbles from too rapid escape of the turpentine or solvents in the varnish, and this would produce defective surfaces in the finished product. lThe best results are secured by a temperature of about 120 degrees Fahr. during the preliminary or setting operation of drying of the varnish which consumes about one hour, and an increase of that temperature to 135 degrees Fahr. during the continued recirculation of the air for a period of twenty four hours, in which the baking of the varnish takes' place. When the volatile gases have been largely eliminated and the baking completed, it is then possible lto raise the temperature of the air circulating over the skins in the drying operation without producing surface defects and the temperature may therefore be raised considerably higher (so long as the leather is not burned) and circulation maintained for a period of nine hours, and in this manner the drying is almost completed, the final removal of all tackiness from the surface of the skin being accomplished by shutting offkthe heat and circulating cold air through the* oven and allowing it to escape tothe chimney by flue 14. In the first or setting operation, in the drying of the varnish, the air and volatile vapors escaping from the oven may be allowed to go to the chimney by way of Hue 14 instead of passing to a condenser; and in place of being' heated to 120 degrees Fahr., the air, employed in this setting operation, may have a less temperature.

`ing the varnish over kIn the last or -nal operation to remove the tackiness, the cooler the air which is circulated through the oven, the more satisfactory the result; but in cases where the absolute humidity of the atmosphere is exceptionally high, it is desirable to lower its relative humidity b y heating it to some extent before circulating through other conditions, this heating of the air will not be necessary or advisable.

Where it is not desired to save the volatile solvent in the varnish, the air which is laden with said solvents may be allowed to escape through the flue 14 by adjusting the valve 16 into the position indicated in solid lines in Fig. 1, performing thereby thesame operation of drying which was carried out in the case of drying the daub coating. In this way there will be some increase in the speed of drying because of the complete elimination of all volatile matters from the drying air at a time when the varnish is in a very fluid or plastic condition. After the main volatile vapors have been eliminated by the drying operation, the valve 16 may be shifted to the dotted position and the air then recirculated with or without the employment of the condenser and the external heater, if so desired. This latter operation is desirable because the recirculation of the air enables the drying operation to be carried on with less loss of heat; and this is material in the operation of my process by a large plant when carried over a considerable period of time.

In actual operation, there is a great saving in time required by my method of drythat required by the process now in general use. For example, the operation of setting and baking by my process requires 25 hours, whereas in the method now in use, the time necessary is 36 hours; and the operation of drying requires, by my method, 12 hours, whereas in the method now in use 36 to 72 hours are actually required, when it is .possible to dry atr all; This latter is most important to be taken into consideration, because the old method being a sun drying process, is dependent solely upon the existence 'of a dry atmosphere and sunshine, two conditions which are .frequently laclng, and because of which, no certainty has heretofore existed in the output in finished leather from a factory. This trouble is entirely obviated by the use of my improved process.

The foregoing description has been di- -rected to a slngle oven which, of course, may

the oven. Under of air from a common source and to deliver municate with the air laden with the vapors to a common escape Hue, or otherwise, as hereinafter eX- plained. f

Referring more particularly to Figs. 3, 4, 5 and 6, a plurality of ovens is indicated at 2, and of these there may be any number.. The upper headers 13 of these ovens comtwo longitudinal conduits 21 and 22 by means of suitable valves indicated at 16, and in this case for convenience,

the valves may bein the `form of slides in place of being pivoted, as shown in Fig. 1.

' The Hue 21 communicates with an upright Hue 14 corresponding to the Hue 14 in Fig. 1, and this ma lead to the chimney. or other outlet to the tmosphere.l A drafd device,

Vin the form of a blower 32, mays-be em ployed to create a suction from t conduit 21 to more quickly withdraw the vapor laden air from the various ovens.

Natural draftmight be sucient in some vuse again 1n passes through the condenser 23 is con veyed by a.. pipe sultable construction, the heated air'may pass 26 to a heater 33 of any and from the heater by a pipe27 to the -suction sidev f a blower 28 by whichthe circulation -of the air may be produced or asas each of the ovens is sisted. The'discharge side o f the blower 28 communicates with a conduit 10 which corresponds to the conduit 10 in Fig. 1. From this conduit the air may pass through the valves 11n into the conduits 10 leading into the chambersS inthe ovens. VThe valve'll erforms the function ofthe valvev l1 inl ig. 1. -In this manner the airgmay be, re-

circulated through'the various ovens over and over again and the vapors of turpentine may be largely removed from the? circulation and'I collected bybeing brought 'into contact with the condens' 24 -in the condenser. In this' way, the drying atmosphere to: which the .skins are subjected is prevented from becomingv saturated or over impregnated atile turpenti-newapors, whose presence would retard and prevent roper ,drying of the skins. The sp p be governed to av mcet'y. Iby'nthe control of the valvess 11, and itisfj'also. evident that provided with independent valves, the speed of circulation in any oven may be varied with respect to the various ovens vwith the valve 11".`

the circulating' system Ito be ""g surface Y the -same reasons as the supply' and eed of circulation may speed of circulation in any other oven. This enables the control of the circulation in the suit the particular condition of the ma erials being treated in the oven at 1any particular time. Moreover, the apparatus may be operated continuously and any oven may be put into or out of operation, or varied in temperature, or speed `of circulation without interference with, or

affecting the operation of any other of the ovens. This-,is important in a plant which employs a large number of these ovens in the carrying on of its ond conduit, parallelto the conduit 10 and may be'put into communication with the conduits 10a of the several ovens by valves, which may, for convenience, be integral This conduit -29 may business. 29' is a sec- 'so y lead to the atmosphere so that fresh air .i

may` be supplied to the several ovens, or any of them, and after acting upon the contents of the ovens, may bepermitted to escape by the Hues 21 and 14 into the chimney, this operation, being substantially that which is preferred to be carried on in respect to the drying of the daub coating of the leather. A branch pipe 30 may communicate with the conduit29 for sup lying fresh air to the suction side of the lower by a valve 31, and by which a given amount of air may bel introduced into circulation at any time to facilitate the drying operation. Moreover, this valve 31 may be opened when it is desired to quickly purify the chambers of any gases or vapors contained within them, and whichv operation would be lperformed'b simultaneously opening the valves 16v to theconduit 21'. In this case and this conduit 30 may be controlled' Y the fresh air would be drawn in through the i conduit 10 into-,the oven or' ovens, and thence outthrough the conduit 21 into the Hue 14 to the chimney. This operation may bev employed as the nal operation in the drying of the lvarnished leather, thou hsthe draft of the conduit 21 would be su cient.'

This vsame action would also enable all of the vapors which might be with the air in driven out of the ovens and pipes generally, into the chimne V `It w1 l1 be observed that the conduit 22 and ,the conduit 10 respectivelyilead from and to the ovens from different directions to insure uniform resistance in thecirculaw1th. the volt'ron through the several ovens, precisely for discharge ends of the Hues 5 in e h oven are respectively at the bottom an topP This feature of uniform resistance of circulation through the plurality 'of ovens becomes im- .portant when twenty-five to one hundred ovens are employed in one plant, because by such arrangement' the operation of any oven or group of ovens cannot, in effect, short circuit the currents of drying medium required to flow through others of the ovens.

In cases where the humidity of the atmosphere ishigh or approximating saturation, as on rainy days, it will be desirable to raise its relative humidity as before stated and this may be done by opening the valve 34 in conduit 35 leading to the heater 33 and closing valve 31l in conduit 30, in which case, by the adjustment of yvalves 11a and 16a, the air, after being heated, is delivered into conduit 10 and thence through the ovens into the conduit 21 and by conduit 14 into the chimney.

I do not restrict myself to any particular details of construction of the oveny or of the connectin flues, or`means for governing or contro ling or inducing the circulation of the air through the ovens and over the stretched leather therein, as these may be varied or modified in many ways without changing or alterin the operation or the results to be accomplished by the carrying out of my improved process.

In the operation of my improved arrangement of the plurality of ovens, the following process may be followed: The leather is stretched by tacking or fastening upon the frames in any suitable manner, and then coated with the daub, which is prepared in the ordinary and well known manner to those familiar with the art of making patent or enameled leather. The frames containing the leather so prepared are then introduced, into thelovens (as indicated in Figs. l and 2), and the tempera-ture of the oven is raised to 120 degrees Fahr., being that required` for drying out the daub coating. The drying operation is facilitated by arranging the valves 11a and 16, forA supplying the heated air under natural or forced draft through the ovens, the constant supply of fresh air passing over the heating coils 12 passing upward through the llues 5 at one side of the ovens, thence horizontally over and under the various stretched skins and their frames, thence into the lues at the opposite side of the ovens, and thence upward into headers 13 and from it into conduit 21 leading to the flue 14 connecting with the chimney. The speed of circulation of the air in this manner should be restricted to exactly that which is necessary, with the heating by the coils 12, to maintain the desired temperature in the oven, which ordinarily should be of approximately 120 degrees Fahr. The maintenance of this temperature may be controlled by the valves ,11a and from the indications of a suitable thermometer extending into the interior of the oven`for indicating its temperature. If the temperature falls too low, the valves 11a should be closed to a greater extent to-restrict the inflow of fresh air, and on. the other hand, should the temperature rise too high, the said valves may be opened to a greater extent; or the steam control valves 21 may be throttled to a greater or less extent to maintain the required temperature. It is somewhat important in this operation not to make too strong a draft of air through the oven, as too rapid a volatilization of the coating on the leather will have tendency toproduce more or less unevenness due to bubbles formed on the surface. This, however, is not so apt to occur in the case of daub coats as with the varnish coats later to be applied to the leather. The circulation thus carried on conveys away from the ovens the volatile ether or other vapors which may be produced, as quickly as they are eliminated from the dau-b coating of the leather, so that the atmosphere in which` the leather is contained is always maintained in a condition which readily absorbs the volatile constituents of the said daub coating, thereby enabling a speedy drying of the material in a uniform and effective manner. After the operation of drying of the daub7 coating has been performed, the 4frames 7 with their leather stretched thereon are withdrawn from the ovens and the daub coated surfaces are pumice-stoned, and thereby brought to the required smooth surface which is necessary in the manufacture of leather of this character. If desired, more than one daub coating may be applied and dried, and the same may be re-pumicestoned, lbut ordinarily this is not necessary. The leather, when thus prepared with the finished daub coating, is next treated t0 a coating of varnish, which maybe of the usual composition hereinbefore referred to. This varnish contains very volatile substances, of which turpentine is the essential one to be considered. The varnish may be of the character heretofore in common use in the manufacture of patent or enameled leather. The skins, carefully coated with the varnish, are then immediately inserted into the ovens, the doors 19 thereof placed in position, and the operation of drying the varnished surface is performed as follows: The valves 16?y are shifted so as to close the outlets from the ovens into the conduit 21 and to open the outlet into the conduit 22; likewise, the valves 11a are shifted so as to close the communication between the ovens and the conduit 29 and open the communication between the ovens and the conduit 10. The blower 28 is then put into operation and the air, preferably` about a temperature of 120 degrees Fahr., is slowly circulated through the ovens, through the condenser 23 and through the heater 33. The turpentine vapors which are liberated from the varnish are conveyed `from `the 'ovens through the conduit 22 into the condenser 23, and are fore desirable to again raise the air to the normal temperaturey by passing it through the heater 33 before being again circulated through the ovens 2. The temperature in.

each of the ovens is independently reguc lated by its own heating coils 12, but by heating the air externally to the ovens, less duty is required of the individual heaters 12, and hence, 'it is moreeasy to regulate' the temperature within thevoven to the de-. sired extent to insure the proper drying operation whereby itwill be as ,speedy as ossible, Xwithout danger of producing lbub les on the surface from too rapidevaporation. After the setting ofthe. varnish has been completed, the temperature off the ovens and air may beyraised to 135 degreesFahr. -or higher and the circulationI continued .as before for a period of twenty four hours,more or less, to bake the varnish'ed kto still further densify the varnished coating. This baking causes the volatile vapors .to be driven ofl'l and the varnish to'be fully set, and after this has been done there is noA further danger of bubbles forming, Or cracking of the varnish by heat, and hence the are then in condition for the next opexation, namely, dryin l The drying 1s accomplished as follows The condense;l may be shut of't' or put out of circuit by pipe 36 having valve 3T, and the temperature of the ovens and air raised to 140 degrees Fahr. or upward and the circulation maintained for a period of about nine hours. While this drying operation is taking place, the varnish having become well set and argely free from volatile constituents, the temperature fnay be considerably raised according to the conditions of the air, I having used in practice temperatures as high as 155 degrees Fahr. with good effect. During this drying 'operation the air may be partly changed by partly opening the valve 34 and the valves 16, so that a portion of the circulating air may beallowed to escape to the chimne fresh a1r admitted into the circulation. This will facilitate the drying, but care should be exercised to prevent the temperature becoming lowered, or a retardation of the process and a corresponding portion of will result. After aboutx nine hours, under the drying operation, the varnish will have become dried, but still retains tackiness, and the valves 16a and 3l may be then so adjusted as to provide means for full escape into the conduit 21 andA thence `to the chimney by flue 14, of the air from the ovens,

while a corresponding amount of fresh cool ,t air is permitted to pass through the pipe 30 and valve 3-1 into the circulation; Instead of the fresh air passing through the blower before passing into the ovens, it may be permitted tov pa directly through the conduit 29, through valves 11'* and conduits 10a into the'ovens. In this final drying to remove tackiness, the air supplied to the ovens is best when in a cool and dry condition; but if it has too'. much humidity, it must be heated first by heater 33 before admittance to the ovens, as before set out. This final operation is ordinarily conducted with the heating coils 12 shut of, but these coils may be employed .separately or in combination with the heater 33, when found advisable to counteractjthe excessive humidity.

During theo erations above described it is to be remem ered that each of the pluralit ,of ovens may be operated as an indeor' any simultaneous combinations of these steps. Each oven is under the general control of heat or cold, but is also under independenty control of temperature by its own heating coils 12. It will thus be seen that all ofthe operations necessary may be carried on at one time in the same set of ovens :Rf merely adjusting the conditions requir and hence all of the workmen may be kept occupied.

The manufacture of the enameled and patent-leather maybe conducted, irrespective of the atmospheric conditions; and the baking and drying may be carried on both day and night, sothat no loss of time will occur waiting for favorable conditions, as heretofore, and which, with the impossibility of manufacturin with assurance of prompt delivery, reliability and uniformity of the finished product, has been the cause of many failures in business. y

Where the saving in the turpentine from the varnish is not deemed desirable, as where the plant is small, then the condenser may be dispensed with, but in this case it is desirable during the baking operation to allow a portion of the turpentine laden airfrom the ovens to escape by the conduit 21 tothe chimney, and supply a corresponding quantity of fresh air into `circulation by pipe or otherwise. The speed of the process is largely the turpentine vapors from the circulating air and this should be done even at a sacrifice of some heat units necessary to raise the y, temperature of the` incoming fresh air.

Where the cost of fuel is low and saving 1n heat not important, then it is preferable to permit the entire baking and drying operations to be conducted requisite temperatures. In this case, the turpentine vapors carried off in the baking operations, may be condensed by the condenser and the air allowed to escape by simply closing the valvej 37 and opening cthe valve 36 in escape flue 38 in connection with the condenser. When this operation is carried on, all of the air which is to be heated may be taken in through pipe 35 when its valve 34 is opened. v

I have shown my apparatus in the form which I have found most effective, and have described my improved process in the way I have preferred to operate under it in the commercial manufacture' of -enameled and patent-leather, but I no not restrict myself to the details of theiapparatus, nor to the specific temperatures or time periods stated, as these may all be varied from the spirit of the invention.

In this application, I do not make claim to the apparatus herein described as the same will form subject matter of a divisional application. l

Having now described my invention, what I claim as new and desire to secure by Letters Patent is y 1. The herein described method of manufacturing leather with an enameled surface from tanned skins having filled surfaces, consisting in coating a` plurality of filled skins in stretched condition with varnish, placing the said stretched varnished skins within a closed oven with the skins arranged substantially horizontally and arranged one above the other, causing the varnish to set at a temperature insufliclent to produce bubbles in the varnish, baking and drying all of the set varnished surfaces of the plurality of skins under the same conditions by subjecting said varnished surfaces simultaneously to equal currents of heated air and withdrawing the vapor laden air from the oven immediately after acting upon the leather, and finally lowering the temperature of the heated air after the baking of the varnished surface of the skins to insure thorough and complete drying and cooling of the same before removing the skins from the oven.

2. The herein described method of manufacturing leather with an enameled surface, consisting vin placing stretched varnished dependent upon the elimination of with freshy air at the without departing skins in a closed oven in horizontal position one above the other and in a quiescent condition, raising the temperature of the oven sufficiently to vaporize the volatile matters of thefvarnish but not burn the leather, circulating air horizontally between the stretched skins at the said temperature, and forcibly removing the vapor laden air from the oven until the leather is approximately baked and dried, then passing cooler air through the oven for lowering the temperature of the oven and cooling the skins and removing all tackine'ss thereof, and finally withdrawing the skins from the oven.

3. The herein described method ofv manufacturing leather with an enameled surface from a skin having a filled surface, which consists in varnishing the filled surface in stretched condition, arranging the stretched varnished skin in a horizontal position within a closed chamber, baking and drying the varnish by passing a current of air over the same at approximately 14() degrees or upward and during the baking operation removing the vapor laden air rom the closed chamber and presence of the leather, and finally removing all tackiness from the dried varnished surface by passing a current of air at much lower temperature over the varnished skin for lowering its temperature and hardening the varnished surface.

4. The herein described method of manu-V varnish, causing a circulation of air through the oven and over the surface of the leather and thereby removing the vapors which escape from the varnish and transferring said vapors to a point outside of the oven to produce a greatly more dense and dry condition of the varnished surface, then raising the temperature of the partly dried leather and subjecting it to a continued current of air at the higher temperature until the varnished leather is thoroughly baked and dried, and finally removing the leather from the oven.

5. The herein described method of manufacturing leather with an enameled surface from a tanned skin having a filled surface, consisting in varnishing the filled surface of 4the leather and placing it while sticky in a closed oven heated to a temperature sufficient to volatilize the more volatile portions of the varnish, causing a circulation of air through the oven and over the surface of the'leather and thereby removing the vapors which escape from the varnish and transferring them finally removing the tackiness of the dried varnished leather by passing a current of cool air over the heated leather to lower the temperature of the oven and cool the leather before removing the leather from the oven.

6. The method of making enameled leather, consisting in coating the leather with varnish, then placing the coated leather in a closed oven, then setting, baking and drying the varnish by subjectlng the leather successively to a medium temperature, a high temperature and finally to a low temperature, and for a greater period of time to the high temperature than to the medium and low temperatures, and during the setting and baking operations removing the vapor laden air rom the oven and supplying fresh heated air in its place.

7 The herein described method of manufacturing leather with an enameled surface, consisting in baking and drying a varnished surface on the leather by causing a forced circulation of heated air to pass over the varnished surface and moving the vapor laden air out of contact with the leather, and regulating the temperature of thelair during the baking and drying operations Without disturbing the leather throughout its entire treatment.

In testimony of which invention, I hereunto set my hand.

R. M. HUNTER.

Witnesses:

A. M. KELLY, ELFREDA KOEMMENICH. 

